A vehicle running by using electricity as a driving force is mounted with a storage battery such as a lead-acid battery, a nickel hydrogen battery or a lithium ion battery. The electric power required when a hybrid vehicle or an electric vehicle is supplied by the storage battery.
The permitted charge power and discharge power of the storage battery respectively vary according to the state of charge. If charging or discharging over the maximum permitted power is performed, overcharging or overdischarging can occur. As the state of charge (SOC) of the storage battery becomes high, the maximum permitted charge power decreases and the maximum permitted discharge power increases. Alternatively, as the SOC of the storage battery becomes low, the maximum permitted discharge power decreases and the permitted charge power increases. In order to safely use the storage battery, the charging and discharging control is required to be performed within a range not exceeding the maximum permitted power.
PTL 1 mentioned below discloses a technique in which, even when a temperature variation occurs among single cells constituting a battery pack, permitted charge and discharge powers suitable for respective single cells are calculated, and charging and discharging control is optimally performed.
PTL 2 mentioned below discloses a method in which a maximum cell voltage value and a minimum cell voltage value are detected, maximum charge power is determined by using the maximum cell voltage value, and maximum discharge power is determined by using the minimum cell voltage value.